The present invention relates to a mobile communication terminal such as a portable phone, a PHS (Personal Handy Phone), or the like, and a channel connection method therefore.
Conventionally, an analogue or digital portable phone is a kind of terminal that forms a radio channel. Communication is made with a calling party in the opposite, which is connected to a public telephone network, through a base station connected to a radio channel network.
This state is shown in FIG. 8. This figure shows a conventional channel connection form. In this figure, the reference symbol 1 denotes a communication terminal of a communication in the opposite side. The reference symbols 2, 3, 4, and 5 respectively denote a public network, a radio channel network, a base station, and a conventional communication terminal.
In the communication terminal 5, one radio unit is mounted in one casing. A radio channel to the base station 4 is formed by using this radio unit. Therefore, no communication can naturally be made through another radio channel while a radio channel is formed by the radio unit included therein.
As another kind of terminal, a dual-mode terminal includes two radio units in one casing and serves as both of an analogue portable phone and a digital portable phone. In this dual mode terminal, the radio unit for an analog portable phone is included in the one same casing, in order to compensate for the drawback that a digital portable phone is usable within a narrow service area. Outside the service area of the digital portable phone, the dual-mode terminal is switched to an analogue portable phone.
This state is shown in FIG. 9. This figure shows a channel connection form of a conventional dual mode terminal. In the figure, the reference symbol 1 denotes a communication terminal of a calling party in the opposite side. The reference symbol 2 denotes a public network. The reference symbols 3a, 3b, 4a, and 4b respectively denote a radio channel network of an A-system, a radio channel network of a B-system, a base station of the A-system, a base station of the B-system, and a conventional dual mode terminal. Note that the A-system is a communication system for an analogue portable phone and the B-system is a communication system of a digital potable phone.
The dual mode terminal 6 has two radio units in order to compensate for the service area of the digital portable phone, as described above. These two radio units do not operate simultaneously but operate singly with respect to the base stations 4a and 4b connected to the radio channel networks 3a and 3b, respectively, thereby forming a radio channel. Accordingly, if a radio channel is formed with one of the base stations 4a and 4b, another radio channel cannot be formed.
As described above, a conventional communication terminal cannot form a plurality of radio channels within one casing. Therefore, when a response is made to a communication request from a calling party, there is a drawback that the communication channel to this calling party cannot be transferred to another communication terminal. To avoid this drawback, the calling party must shut off the channel which is currently connected to the called communication terminal and must further make an operation of dialing up the telephone number of another communication terminal.
That is, the calling party must shut off the radio channel to the communication terminal (the called side) connected to a base station and must further input the telephone number of another communication terminal to make another call, so complicated operation is required. Also, the calling party must pay an extra communication charge for this second call.